1. Field
Exemplary embodiments of the present invention relate to a memory and a memory system.
2. Description of the Related Art
A memory cell of a memory includes a transistor serving as a switch and a capacitor that stores a charge (data). ‘High’ (logic 1) and ‘low’ (logic 0) data values are determined depending on whether there is charge in the capacitor of the memory cell, that is, whether the terminal voltage of the capacitor is high or low.
Since storage of data indicates the accumulation of a charge in the capacitor, in theory energy is not consumed during data storage. However, since the initial charge stored in the capacitor is reduced due to current leakage at the PN junction, as well as other places of a MOS transistor, data may be lost. In order to prevent such loss, data in the memory cell is read and the memory cell is recharged before data is lost based on read information. Only when such an operation is periodically repeated can storage of data be maintained. This memory cell recharge process is called a refresh operation.
FIG. 1 is a diagram illustrating a part of a cell array included in a memory in order to explain a word line disturbance phenomenon, ‘BL’ indicates a bit line.
In FIG. 1, ‘WLK−1’, ‘WLK’, and ‘WLK+1’ in the cell array indicate three word lines arranged in parallel with one another. The word line WLK marked by ‘HIGH_ACT’ indicates a word line that has had a large number of activation times or a high activation frequency, and the word lines WLK−1 and the WLK+1 are word lines arranged adjacent to the word line WLK. ‘CELL_K−1’, ‘CELL_K’, and ‘CELL_K+1’ indicate memory cells electrically coupled to the word lines WLK−1, WLK, and WLK+1, respectively. The memory cells CELL_K−1, CELL_K, and CELL_K+1 include a cell transistor TR_K−1 and a cell capacitor CAP_K−1, a cell transistor TR_K and a cell capacitor CAP_K, and a cell transistor TR_K+1 and a cell capacitor CAP_K+1, respectively.
In FIG. 1, when the word line WLK is activated and precharged (or deactivated), voltages of the word lines WLK−1 and WLK+1 rise and fall due to a coupling phenomenon occurring between the word line WLK and the word lines WLK−1 and WLK+1, resulting in an influence on the amount of charge stored in the cell capacitors CAP_K−1 and CAP_K+1. Therefore, when the word line WLK is excessively activated, precharged, and is toggled between an activated state and a precharged state, data stored in the memory cells CELL_K−1 and CELL_K+1 may be lost due to a change in the amount of charge stored in the capacitors CAP_K−1 and CAP_K+1.
Furthermore, electromagnetic waves generated in the toggling of the word line between the activated state and the precharged state causes the transfer of electrons to/from electrically coupled memory cell capacitors in adjacent word lines causing data loss.